Cracking the Coding Interview Hard Problem (add function without use of '+') - First Attempt

public class Adder 

{

/*

Ci  a  b    o    c

0   0  0    0    0

0   0  1    1    0

0   1  0    1    0

0   1  1    0    1

1   0  0    1    0

1   0  1    0    1

1   1  0    0    1

1   1  1 1    1

*/

// 4 bit adder

static public int add(int a, int b) {

int [] output_logic  = {0,2,2,1,2,1,1,3} ;

int mask = 1 ;

int result = 0;

int carry_in = 0;

int carry_out ;

int output ;

int input_logic_index ;

int abit ;

int bbit ;

int bit_result ;

// 1 bit adder

abit = (1 & a) ;

bbit = (1 & b) ;

input_logic_index = (carry_in << 2) | (abit << 1) | (bbit << 0) ;

output = output_logic[input_logic_index] ;

carry_out = (output & 1) ;

bit_result = ((output & 2) >> 1) ;

carry_in = carry_out ;

result|=(bit_result<<0) ;

a>>>=1 ; b>>>=1 ;

// 1 bit adder

abit = (1 & a) ;

bbit = (1 & b) ;

input_logic_index = (carry_in << 2) | (abit << 1) | (bbit << 0) ;

output = output_logic[input_logic_index] ;

carry_out = (output & 1) ;

bit_result = ((output & 2) >> 1) ;

carry_in = carry_out ;

result|=(bit_result<<1) ;

a>>>=1 ; b>>>=1 ;

// 1 bit adder

abit = (1 & a) ;

bbit = (1 & b) ;

input_logic_index = (carry_in << 2) | (abit << 1) | (bbit << 0) ;

output = output_logic[input_logic_index] ;

carry_out = (output & 1) ;

bit_result = ((output & 2) >> 1) ;

carry_in = carry_out ;

result|=(bit_result<<2) ;

a>>>=1 ; b>>>=1 ;

// 1 bit adder

abit = (1 & a) ;

bbit = (1 & b) ;

input_logic_index = (carry_in << 2) | (abit << 1) | (bbit << 0) ;

output = output_logic[input_logic_index] ;

carry_out = (output & 1) ;

bit_result = ((output & 2) >> 1) ;

carry_in = carry_out ;

result|=(bit_result<<3) ;

a>>>=1 ; b>>>=1 ;

// 1 bit adder

abit = (1 & a) ;

bbit = (1 & b) ;

input_logic_index = (carry_in << 2) | (abit << 1) | (bbit << 0) ;

output = output_logic[input_logic_index] ;

carry_out = (output & 1) ;

bit_result = ((output & 2) >> 1) ;

carry_in = carry_out ;

result|=(bit_result<<4) ;

a>>>=1 ; b>>>=1 ;

return result  ; //| carry_out;

}

static public void main(String [] args) {

int failed = 0 ;

for (int i = 0 ; i < 15 ; i++ ) {

for (int j = 0 ; j < 15 ; j++) {

int fullResult = add(i,j) ;

int compare = i + j ;

if (compare != fullResult) {

System.out.println(" i, j " + i + "," + j + " full result = " + fullResult + "<->" + compare + "failed") ;

failed++ ;

}

}

}

System.out.println("Failure count " + failed ) ;

return ;

}

}